div class=”ChapterContextInformation”>
26. Pain Relief in Labor
The delivery of the infant into the arms of a conscious and pain-free mother is one of the most exciting and rewarding moments in medicine—Moir
Sources of pain during labor
Severity of labor pain
Currently there is a shift in obstetrical anesthesia practice with emphasis on overall management of patient care including quality of analgesia rather than simple focus on pain relief only [3]. Better understanding of physiology as well as pharmacology along with the coming up of obstetric anesthesia as a subspecialty has led to an absolute advancement in the field of labor analgesia. Regional analgesia for labor has today become a part of standard obstetric care.
26.1 Effects of Labor Pain
Painful contractions result in maternal hyperventilation, causing respiratory alkalosis with a leftward shift of the oxyhemoglobin dissociation curve and increased maternal hemoglobin affinity for oxygen. Hypocarbia also leads to hypoventilation in between contractions, which may further decrease the maternal PaO2. Increased oxygen consumption which occurs during labor along with hypocarbic uteroplacental vasoconstriction is a potential cause of fetal hypoxemia. Increases in cardiac output and vascular resistance may increase maternal blood pressure. The response of sympathetic stimulation to pain also leads to increase in levels of catecholamines which can depress the uterine activity and uteroplacental circulation. Effective labor analgesia benefits most the high-risk parturient, i.e., those with preeclampsia or cardiac disease and those with marginal uteroplacental circulation and function by attenuating these responses.
26.2 Methods of Pain Relief in Labor
26.2.1 Nonpharmacologic Methods
Expectation of the patient concerning labor influences the childbirth experience.
The concept of natural childbirth was given by Eappen and Robbins in 1940 which consisted of teaching relaxation techniques and the elimination of fear to prevent labor pain [4]. Fernand Lamaze introduced psychoprophylaxis involving focusing on objects or breathing exercises to distract from pain, along with the use of conventional analgesic drugs [5]. Although taught extensively, there is a lack of scientific validation of the efficacy of these methods. Patients have been found to use coping techniques in the early first stage of labor but less so as labor progresses. Prepared childbirth by most modern instructors provides information about the elementary physiology of pregnancy and delivery with the aim to reduce fear and teach relaxation and breathing exercises.
Nonpharmacologic methods are preferred by some patients for pain management during labor. Acupuncture has been found to be useful in treating postoperative analgesia after cesarean section but shown poor results in controlling pain during labor [6]. In a meta-analysis to observe the efficacy of acupuncture, it was found that acupuncture had a small but statistically significant effect on labor pain, but the effect lasted for only 30 min [7].
A Cochrane review on massage for labor pain relief found that though pain decreased marginally in the massage group in the first stage of labor however no difference was seen in the second and third stages of labor [8].
Hypnosis as a relaxation technique has also been used for pain relief in labor. However no conclusive evidence is reported in literature. Other nonpharmacologic techniques such as transcutaneous nerve stimulation (TENS), hydrotherapy, presence of a support person, intradermal water injections, and even biofeedback have all been used for pain relief during labor.
26.2.2 Pharmacological Treatment of Pain in Labor
26.2.2.1 Inhalational Analgesia
Inhalational agents were the earliest to be used for labor analgesia in modern times. The technique involves the inhalation of subanesthetic concentrations of an agent while the mother remains awake with intact protective laryngeal reflexes. It can be used alone or in combination with other methods of analgesia. Increasing usage of volatile anesthetics in childbirth resulted in rising incidence of side effects especially neonatal depression and maternal gastric aspiration [9, 10]. This leads to the origin of fasting measures, and the guidelines recommended by Mendelson became cornerstones of obstetric anesthesia practice.
Nowadays volatile anesthetics are not very popular for pain relief in labor although nitrous oxide is still being used in few less developed countries. It is mixed with O2 in a 50:50 ratio or slightly more for patient inhalation via a demand valve through a low-resistance breathing system. It takes 45 s for the analgesic effect to be achieved; hence the parturient should start breathing Entonox at the start of a contraction to achieve desired brain concentration at the height of contraction. Deep, slow breathing and abstaining from Entonox between contractions is encouraged. Studies have demonstrated different response to inhaled N2O varying from moderate analgesia [11, 12] to no difference in visual analogue pain scores [13]. The analgesic effect of N2O may be confounded by sedative and relaxing effects that benefit the laboring woman. Use of N2O in O2 is safe and does not cause hypoxia, unconsciousness, or loss of protective airway reflexes [14] which is commonly seen with opioids. Also there is no effect on uterine contractility and neonatal depression irrespective of duration of use.
The efficacy of small concentrations of halothane, enflurane, isoflurane, desflurane, and sevoflurane in labor, alone and in combination with nitrous oxide, has also been demonstrated [15–17]. As sevoflurane has early onset and short duration of action, it is the most preferred inhalational agent for labor analgesia and can be given as patient-controlled inhalation analgesia. But with the use of inhalational agents, environmental pollution is always a concern as well as risk of loss of consciousness and compromised airway reflexes leading to aspiration [18].
26.2.2.2 Parenteral Agents
Many agents that activate the μ-opioid receptors provide good pain relief during labor. Opioids are widely available and relatively cheap, hence commonly used. However as there is placental transfer of opioids, their use in labor is a compromise between effective analgesia and unwanted side effects.
Meperidine is the most commonly used long-acting opioid in obstetric practice worldwide [19]. Maternal T1/2 of meperidine is 2–3 h but is 13–23 h in fetus and newborn due to an active metabolite normeperidine which crosses the placenta and causes respiratory depression. Newborn is at greater risk with increased dose and shorter dosing intervals [20].
Morphine is no longer used for labor analgesia as it causes excessive maternal sedation and significant neonatal respiratory depression with loss of fetal beat-to-beat variability.
Butorphanol and nalbuphine are mixed agonist/antagonist opioids which are very popular, especially in the USA, for the relief of labor pain. These drugs do cause respiratory depression but exhibit a ceiling effect with increasing doses. The dose of butorphanol is 2–4 mg intramuscularly but is associated with 75% incidence of transient sinusoidal fetal heart rate pattern. For this reason nalbuphine 10 mg i.v. has become the drug of choice in many institutions though it causes some maternal sedation.
Nowadays, shorter-acting fentanyl and ultrashort-acting remifentanil are gaining popularity for pain relief. Fentanyl is a highly lipid-soluble synthetic opioid with 100 times analgesic potency in comparison to morphine. Its onset of action after intravenous administration is within 2–3 min with a short duration of action and no major metabolites thus making it a good drug for labor analgesia. In small doses it does not cause any significant difference in neonatal Apgar scores and respiratory depression [21]. Because of its favorable pharmacokinetics and pharmacodynamics, patient-controlled intravenous analgesia (PCA) is also a suitable mode for fentanyl administration.
Remifentanil has emerged as an alternative to regional analgesia for patients with contraindications and for those unwilling for regional anesthesia. It is an ultrashort-acting opioid and has a favorable safety profile. As it is metabolized by placental esterase, hence fetal blood concentration is less. Moreover esterase enzymes are mature in the fetus so the metabolism of remifentanil is unaffected [22]. The recommended dose of remifentanil is 20 μg intravenously. During remifentanil infusion, it is important to monitor for maternal hypoventilation as episodes of oxygen desaturation are observed.
Ketamine, a phencyclidine derivative, in doses of 10–20 mg intravenously, also produces good analgesia in 2–5 min without loss of consciousness. Doses up to 1 mg kg−1 do not cause fetal depression and have no effect on uterine tone. Although its short duration of action makes ketamine unsuitable for first-stage analgesia, it may be effective just prior to vaginal delivery or as an adjuvant to regional anesthesia. The potential for unpleasant psychomimetic effects however must be borne in mind though the incidence is minimal with low doses.
In case of parenteral analgesics, intravenous administration is superior to intramuscular injection as there is less variability in peak plasma concentrations and faster onset of analgesia. Patient-controlled analgesia (PCA) is now widely used in pain relief. Suggested advantages of PCA are better analgesia at lower doses, resulting in less maternal respiratory depression, less placental transfer, less emesis, and higher patient satisfaction. Meperidine, fentanyl, and the mixed agonist/antagonist nalbuphine are the most frequently used opioids for PCA administration.
26.3 Neuraxial Analgesia
26.3.1 Epidural Analgesia
Epidural analgesia for labor was started by Stoeckel in 1909 when he gave caudal epidural anesthesia in 141 cases. Since then, lumbar epidural analgesia has been frequently used for labor and has become the gold standard for pain management in obstetrics [23]. Neuraxial analgesia is the most effective method of intrapartum pain relief with least depressant effect on the parturient and fetus in current practice [24]. Epidural analgesia also offers versatility in the level and duration of effect. Moreover segmental lumbar analgesia can be titrated for the first stage and extended into the sacral segments for the second stage of labor. By providing effective pain relief, epidural analgesia attenuates the adverse physiological responses to pain. In addition, effective epidural analgesia reduces maternal catecholamine levels, increasing intervillous blood flow and resulting in improved uteroplacental perfusion [25]. A much larger beneficial effect is seen in patients having preeclampsia [26]. Local anesthetics, at clinically used concentrations for neuraxial blocks, do not have a direct effect on uterine activity. Neonatal effects may occur, indirectly, from reduced uteroplacental perfusion due to hypotension. The duration and severity of maternal hypotension is important factor in determining fetal hypoxia and consequent neonatal neurobehavioral changes.
Preprocedural assessment for risk factors for regional analgesia and general anesthesia is recommended. Although any laboring woman has the potential to require cesarean section and theoretically should be kept fasting, labor as such takes many hours so adequate nutrition and hydration to the parturient has to be ensured. While balancing these two considerations, the American Society of Anesthesiologists (ASA) has recommended that clear fluids be allowed during the administration of regional analgesia and labor and a period of absence from solids is not required before the placement of regional analgesia.
26.3.1.1 Indications
Current ASA guidelines as well as ACOG committee recommend that maternal request for pain relief during labor is sufficient indication for any sort of intervention and the decision should not left on any degree of cervical dilation [27]. However, there are some categories of patients who will obtain specific benefits. Epidural analgesia decreases the hemodynamic effects of contractions as well as those due to pain response, which is desirable for patients with hypertensive disorders, asthma, diabetes, and cardiac and intracranial neurovascular disease. Epidural analgesia is specifically indicated when general anesthesia involving intubation is suspected to be difficult, as the block can be extended should operative intervention become necessary. Obstetric indications include prolonged labor, oxytocin augmentation of labor, and any factors that place the parturient at high risk for cesarean section. Fetal indications include prematurity, breech presentation, and multiple gestation, as greater control of delivery is possible and the depressant effects of systemic opioids are avoided.
Epidural has frequently been blamed by the obstetricians for increased rate of operative delivery. However the Cochrane Database trials have clearly stressed that epidural analgesia does not significantly impact the risk of cesarean section. In two meta-analyses of randomized trials, patients who received or did not receive epidural analgesia were compared, and no relationship of epidural and increased cesarean section was found [28]. However regional analgesia does increase the duration of labor by an average of about 1 h, and also there is increased incidence of occipitoposterior position as well as increased chance for augmentation of labor with oxytocin. However the low-concentration mixtures which are used nowadays have resulted in decreased incidence of these undesirable effects [29].
26.3.1.2 Contraindications
Absolute contraindications to neuraxial analgesia
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
